Electric system embodying coldcathode gaseous discharge device



1949 K. J. GERMESHAUSEN ELECTRIC SYSTEM EMBQDYING COLD-CATHQDE GASEOUS DISCHARGE DEVICE Filed Oct. 17, 1945 95 &

INVENTOR. Kennel J Germes/zausefi ATTORNEY.

times ranging from to 10 seconds.

Patented Dec. 27, 1949 UNITED ELECTRIC SYSTEM EMBODYING COLD- CATHGDE GASEOUS DISCHARGE DE- VICE 7 Claims.

The present invention relates to electric systems embodying arc-discharge or gaseous-discharge tubes provided with cold cathodes the cathode emission of which is obtained from a small bright spot on the surface of the cathode, known as a cold-cathode spot. The present application is a continuation-in-part of application, Serial No. 538,467, filed June 2, 1944, now abandoned.

Tubes of the above-described character are used, for example, for the production of very intense short flashes of light, in stroboscopic work and photographyand for the control of heavy currents of brief duration. The duration of the current pulses,-and the frequency with which they occur, depend on the application. In some work, there may be as many as several thousand pulses per second; in other applications, they may occur atintervals of minutes, or even hours. cal application, the cathode may be called upon to deliver several thousands of amperes, during These currents may be obtained from a small electrode,

' perhaps /8 inch in diameter and T 5 inch long.

The life of tubes of the above-described character is usually limited by the erosion resulting from the sputtering away of the cathode material, due to the intense ion bombardment and heat in the region of the cathode spot. This sputtering is particularly severe when interrupting high currents in aninductive' circuit, such as occur in very powerful flashlamps for photoface layer of low work-function, such as an oxide of one of the alkali, alkali-earth or rare-earth metals. In operation, however, these thin layers are quickly sputtered away again,'exposing the base metal.

The sputtering rate of various metals, partic-- ularly tungsten, is greatly dependent also on the type of gas filling in the tube. The sputtering rate of tungsten in air, for example, may be as low as 2 to 3 milligrams per ampere-hour; while,

In-what may be regarded as a typifor the rare gases, the sputtering rate may be as high as '70 to 80 milligrams per ampere-hour. The low sputtering rate obtained with air is dependent on the presence of the oxygen in the the surface of the tungsten and this, in turn, lowers the sputtering rate.

In most tubes for the production of flashes of light and for control purposes, the presence of oxygen in the gas is undesirable from the standpoint of tube characteristics. Also, the oxygen disappears or cleans up rather rapidly, thus causing changes in the tube characteristics.

In some tubes for control purposes, it is desirable to fill the tubes with hydrogen, because of its very rapid de-ionization and high breakdown strength. The hydrogen precludes the formation of protective oxide layers and, hence, .causes very rapid sputtering.

, An object of the present invention is to provide a new and improved electric system embodying an arc-discharge or gaseous-discharge device provided with a cold cathode that, operated to pro- .duce a cold-cathode arc discharge, rather than as a thermionic cathode, shall be less subject to sputtering.

Other and further objects will be described hereinafter and will be particularly pointed out in the appended claims.

Toward the attainment of these ends, in accordance with a'feature of the present invention, a suitable compound of low work-function, such as barium oxide, for facilitating the easy emission of electrons, is uniformly sintered and bound together into a unitary mass with a substance, such as tungsten, of high melting temperature, that is highly resistant to sputtering. Under some circumstances, a binding medium may be employed for soldering or otherwise binding the parts together; under other circumstances, no binding medium at all is necessary,

in which event, the entire electrode may be constituted of a uniform mixture of tungsten with a suitable material of low work-function. A surface of the uniformly-sintered and-bound-together mass is thereby continuously presented that combines the sputtering-resistant properties of tungsten with the properties of the said material of 10W work-function, regardless of the wearing away of the surface.

The invention will now be more fully described in connection with the accompanying drawings, in which Fig. 1 is a front elevation of a cathode electrode embodying the present'invention; Fig. 2 is a diagrammatic View illustrating a sintering method; and Fig. 3 is a longitudinal section of a flash-lamp embodying the invention, shown connected into a preferred circuit.

The illustrated flash-tube embodies an elongated light-permeable gas-tight glass-bulb jacket or envelope 92, cemented at 24 to a fiat insulating base plug 94 provided with three lead-in pin terminals 6, l4 and I2 projecting exteriorly thereof. A flash-lamp 18, that may be filled with an inert or reducing gas, such as krypton, hydrogen or any other suitable substantially non-oxygen-containing gas,-is 'm ountedin thee r1y:el; pe;92 I

The fiash ianip m shown neue'any coiled, and provided with two electrodes, constituted of a cathode I and an anode 9, connected, respec-" tively, to the terminals 6 and I2. 'Iheparts are held permanently steady in eer'reet position, arfd properly lined up, in the bu1b92', yniearisof suitable metal spreaders 20. One end of a highvoltage spark trigger or trip-wireelectrode I7 is connected to the terminal i 4, its other end is soldered or otherwise jdiri'edto'one or both ends of a metal ribbon or band supportl9 that is mounted over a plurality of the coils or turns ofuthe helical-tube fl l l8 er" I i by conductors i 'p 'finma e n- 'f'j the condenser l I by denser i ii may bej con- 'riable currentlim- O' afi'o1 gepf, .is y, r en up y, h Loa s n r 25,

,cgnnected to the condenser Ii through a' rectifi jlt', "fi1ter'"co "illustratedanfd dscribedlin' the said Letters Patent 2,277,697, by means of an automatically operjetted contactor 85, that is connected across the .anode or plate and the grid 4 by conductors f 9' 3""ah'tlf91'ir cries with a blocking condenser 'ef'sistor 91, in parallel. The conbe actuated by the object being phDtog-raphed; ''Further details, together with a fuller description of the circuit connections, are

d sch"argethroughgthe fla "electrodes; "The time describedintrie said Letters Patent 2,277,697.

, Asturther described in the said Letters Patent 2,277,697, a voltage surge of the secondary windin j 98 of riner 3B is applied to the 1 r "thetube' lja; The l'i'i ghr'lii "i ii 'rffzes' the g gs in the taliingfp pegrapl s. I

'Owi 'o the brie-s Voltage pulse thus 'impres'sd lliyi ej; enaenser risepween meanbes and the cfold' cathode 7, 'currentpasses betyveen the anode ll and-the cathode I continuallybiit-interruptedly to setup 'Eoiitinually'tlischarges' of arocharacteristic" betweri'tlie cathod'e 1' andthe anode "9. It is of amperage'sufiiciently high'to produce a potential gradient on arelatively small-areaonly er the"before described"surface of the cathode 'T' hig'henoug'h to" form-a cathodespot on the l the temperatures: at-wh-ich substantial thermionic P i fiemi s e n hJ Germeshausen.

ted .t e fiiie e st als fage therefrom. The cted', in series" with a 'e nueh i' i c lslup r fi rt e i f Th f i j r ga 8 "maybef so p'roperu' ea thalt'a desiredfyoltage racrosstheterminals 8 iT th'f terminals 1 l dfid n 91 ransfornier' :Olne

ted tothejterwave a e s a iee' s ar "cold cathode'ga'seousprise an evacuated glass elope' containing sevan anode or plate SQaiidone or more grids, inner value o t sa urre t illeYq h P relatively low that the heat produced is insufiicint emissiorr'may'be produced from the-cold cathode;

and to produce afall of cathodepotential lower 1 than that oco'urrin in' a; glow discharge. cold- 11 cathode spot may thus be'continually but interrupted ly formed on fthe cathode. The average ttxheatthe coldcathode' appreciably; It is suificiently low, indeed, so that'its'root-mean-square peatedly heavy currents of brief duration are thus produced.

, i lb d r el l em; e ra e namelypa' solid cold cathode ra1 ,.-th, i he heati ,qu r n through the tllbegis low enough sotlf'at the'avera'g'e'temp'era- "l'i' 'r' heccld cathode e atwhi'ch substann g 2 'mion'icf cathode emission maybe" produced from the cold cathode 1. Re-

, In ,aeeeraaaeeitijfin e rj'eamr of "the present inventiddthe' cathode elbtrbddihay be constituted @1 00 parts u e te e e i p barium peroiiide' d part cobaltpowd'er by weight. esas a' binder, and it be replaced 15y Qn' ckel copper, or'any other suitable pander; Ur'fdier," certain" circumstances, 701v as herei fter explained; the binder may be 'Ifo 'msiir'ethergug n i-firing; and to reduce the izej theseingredients 2'4 hours; preferably in an inert veiiiefei'suen as carbofitetraclilori'de.

After milling and removal of the carbon tetrachloride by filtering, the resulting powder is pressed into the desired shape in molds (not shown) at pressures on the order of 20 to 40 tons per square inch. At these pressures, a very dense compact pill 3| is obtained, which is strong enough to be handled before sintering.

The electrode pills 3| are then placed in a refractory furnace 34, surrounded by an electrical heater 35, enclosed in heat insulating material H5.

The sintering may be carried out by heating in the furnace 34 in a vacuum, or an inert gas, to prevent oxidation or chemical combination with the materials of the electrode. It is preferred, however, to use a reducing atmosphere, such as hydrogen, since it will remove undesirable nickel and tungsten oxides, and allow better sintering. The hydrogen may be caused to flow into the furnace 34 by way of a gas inlet 43, and out of the furnace through an exit 4'5. The hydrogen is thus caused to fiow through the furnace 34 and around the electrodes during the sintering process.

The electrodes are brought slowly to the sintering temperature. The barium peroxide decomposes, leaving barium oxide; and, at some higher temperature, depending on the composition of the electrode, the pill 31 will sinter into a very strong material.

The proportions of the tungsten, the barium oxide, and the cobalt may be varied over rather wide limits without seriously affecting the properties of the resulting sinter. In general, since the binder represents a relatively nonrefractory material, the quantity of binder should be kept as low as possible, consistent with good bonding and electrical conductivity of the resulting sinter.

The percentage of binder needed to secure good bonding will depend on the percentage of the material of low work-function employed and, to some extent, on how finely divided, uniformly sintered, and bound together the binder and the low-work-function material are. The percentage of binder will also depend on the sintering temperature.

Mixtures containing 100 parts tungsten, 10 parts barium peroxide, and 10 parts nickel or cobalt, or, say, 80 percent tungsten, 10 percent barium peroxide, and 10 percent cobalt, maybe sintered satisfactorily at temperatures of approximately 800 C. to 1500 C., with an optimum temperature of 1000 C. to 1200 C. By reducing the barium peroxide to 1 percent or 2 percent, employing 98 percent to 99 percent tungsten, good sintering may be secured, without the use of any binder, at temperatures on the order of 1500 C.

to 1600" C. or higher. The binder may thus not be needed at all; the tungsten and barium oxide or their equivalents are the substantially essential elements. If the mixture contains 91 percent tungsten, 8 percent barium peroxide, and percent cobalt, the sintering temperature employed may be 1500 C. or higher.

When the percentage of barium peroxide is much over 10, to say 15, the resulting sinter may prove to be weak mechanically, so as to wear very rapidly. If the percentage of barium peroxide should be reduced to a very low value, less than 1 percent to 2 percent, there would not be enough material of low work-function to produce the desired low wear rate.

The proportions will not be materially varied if molybdenum or tantalum be substituted for tion, will reduce the sputtering rate.

the tungsten as the refractory material highly resistant to the sputtering.

The major portion of the cold cathode may thus be constituted of a substance selected from the group consisting of tungsten, molybdenum and tantalum and a suitable material of low work-function.

In general, a high percentage of binder and a low percentage of barium peroxide will make a mechanically strong sample that is both ductile and workable. For the uses of the present invention, however, ductility is not important. Itv is therefore possible to use less binder and more barium peroxide or material of low workfunction.

When the percentage of barium peroxide is: above about 6, and the binder, as cobalt or nickel, is below 5 percent, the resulting sinter is rela-- tively non-ductile. It should therefore be pressed and sintered into the desired form, as; before described.

The sintered electrode 3| may be fastened toa steel or other support 32, by soldering or welding. The support 32 is joined to a rod 33 of tungsten or other material suitable for sealing into the bulb of the flashlamp [8. If the support 32 is of material with a low coefficient of expansion, such as tungsten or molybdenum, approximately matching that of the sinter, the sinter may be pressed onto the support, and sintered thereto, at the same time that the electrode 3| is sintered.

Instead of the barium peroxide, barium carbonate, strontium carbonate, calcium carbonate,

\ or mixtures of these three carbonates may be used as the source of material of low work-function. What is sought after is the barium, the strontium, or the calcium oxide. Other compounds of barium, strontium and calcium that will break down to yield the oxide, on sintering, may therefore equally be used. A substance selected from the group consisting of the oxides of barium, strontium and calcium has been found to be very satisfactory.

In general, the oxides or other compounds of the rare-earth or alkaline-earth groups of elements, classed as materials of low work-func- Not all the alkali, alkali-earth and rare-earth compounds may, however, be employed effectively. Sodium, potassium and caesium compounds, for example, are too volatile to use effectively at the high temperatures of these sinters; they might become lost during the sintering process. Oxides of thorium, aluminum and beryllium, again, reduce the sputtering rate of tungsten. They are not, however, nearly so effective as barium.

With a cathode of this type, the rate of Wear is very low, on the order of 1 to 2 milligrams per ampere-hour even for gas fillings containing no oxygen, such as the rare gases, or hydrogen.

The use of these sintered electrodes in flashlamps of the type shown in Fig. 3 has resulted in a great improvement in life. The life of these tubes was previously limited by darkening of the glass, due to sputtered material from the cathode, resulting in a serious loss of light after about 20,000 flashes. With the sintered electrode of the present invention, on the other hand, there is no appreciable darkening, even after more than 100,000 flashes; and this despite the fact that the emission of the cold-cathode electrode is of the order of thousands of amperes per square centimeter. In other cases, lamps or control tubes that were impractical with other electrodes, due

- toelectrode wear; have been-made 'successtuliy with the new sintered electrode of-the present invention.

Modifications willoccur-to persons skilled-in the art, and all such are-considered to fall within the spirit and scope-of the invention,- as defined in the appended claims.

' What is' claimed V 1. An electric system having, iii-combination,

a gaseous-discharge device having" an envelope containing a gas in which are disposed ananode and a cold cathode the'majonpcrtion of which and of a surface thereof" are constituted-of a substance selected from the groupconsistingof tungsten, molybdenum and tantalum uniformlysinteredand bound together into a-unitary :mass with an oxygen-containing compound selected from-the group consisting: of barium; strontium and calcium, a relatively small cold-cathode spot being adapted to be formed on the-said surface to produce the emission of electrons from the cold cathode at temperatures very I substantially below the temperatures at which substantial thermionic emission may beiproducdfrorn the cathode a brief voltage pulse of magnitude sumcient to form the relativelysmall -cold-cathode -.spot on the said surface of the cold-cathodebht insuffic-ient to heat the cold cathode to a terriiperatu-re at which substantial thermionic emission may beproduced from the cold cathode,

gether into a unitary mass with about "1'5 partsito 1 ---.part, respectively, of barium oxide and with about a gaseous discharge device having an -envelope containing a gas in which are disposed an anode and a cold cathode the major portion'of which and of a surface thereof are constituted'of'a substance selected from'the group consisting ofgtung-v sten, molybdenum andtantalum uniformly sintered and boundtogether into a unitary mass with an oxygen-containing compound selected from the group consistingof"barium;fstrontium' and calcium and with a bindciga relatively small 'coldcathode spot being adapted'tdbe' formed on 'the said surface to produce the emission of electrons from the cold cathodeat' temperatures very substantially below the temperatures at'which'substantial thermionic emission" may be produced,

from the cold cathode; andm'eans forimpress'ing between the'anode and theca'thode a brief'voltage pulse of magnitude sufficient tofo'rni the relatively small cold-cathode spot on" the'said' surface of the cold cathode'but' insufiicie'nt to heat the cold cathode to a temperatureatwhicn substantial thermionic emissionmaybe produced emission of electrons from the cold cathode at" temperatures very substantially belowthe' temperatures at which substantial thermionic emission may be produced-fromthe cold cathoddand means for impressing b'etween' the anode and the '1 per c'entof nickel, a relatively small cold-cath- Jode spot being adapted to be formed onthe said surface to produce the emission of electrons from the cold cathode; at temperatures very substantially'below the temperatures 'atwhich substantial thermionic emissionmay beproduced' from the cold cathode, and means for impressing between the anode and the cathode a brief voltage: pulse of magnitude sufficient to form the relatively small com-cathode spot on the said surface of the cold cathode but insuificient to heat the cold cathode to a temperatureat which substantial thermionic emission may beproduced fror'nfthe cold cathode, thereby to pass an electricdischargebetween the anode and the cathode through the'gasl 5. An electric system having, in combination, a gaseous-discharge device having an" envelopecontai'ning a gas in which are disposed ananode and a cold cathode the major portion ofwhich and of a surface thereof are constituted of a's'ub'stance selected from the groupjconsisting of tungsten, molybdenum and tantalum uniformly sintered and bound together into a unitary mass with an 'oiiygen containing compound selected from the "gr'oupconsisting of barium, strontium'and calcium, a relatively small cathode spot being adapted to be formed on the saidsurface'to'pro- *duce the emission of electrons'fr'om the cold catho'deat'temperatur'es very substantially below 'the temperatures at which substantial thermionic emission may be producedfrom the c'o'ldcathode,

j a cdn'den'ser, means connecting the condenser to the anode and the cathode, means for charging the condenser, and niea'ns'for discharging" the condenser between the anode and the cathodeto impress therebetween a brief voltage puns-or magnitude sufficient to form the relatively small cold-cathode spot on the said surface of the cold cathode but insufficiently to heat the coldcathode to a temperature at whichsubstantial ther- "mionic emission may be produced fromthe'cold cathode, thereby to-pass an'electr'ic'discharge between the anode and't'h'e cathode through thegais.

- a--=gaseous-'discharge .device'having an envelope l 6; An electric system having, in" combination,

containing a gasin which are disposed an 'ano'de and a'cold' cathode themajor'portion-ofwhich and'of a surface thereof are constituted of about to 99 parts tungsten uniformly sintered and bound together into a unita-rymasswith' about 15partsto 1 part;respectively,'ofbarium oxide, a relatively small cold-cathode spot being 1 adapted to be formedonthe said surface'toproduce the emission of electrons from: the cold cathode at temperaturesvery substantially below the temperaturesat which substaritialthermionic emission may be produced from} the'cold cathode, a condensenmeans for 'connecting the condenser to the anode and the cathode,*means for charging the condenser, and means for discharging the condenser between the anode and the cathode to impress therebetween a brief voltage pulse of magnitude sufficient to form the relatively small cold-cathode spot on the said surface of the cold cathode but insufficient to heat the cold cathode to a temperature at which substantiai thermionic emission may be produced from the cold cathode, thereby to pass an electric discharge between the anode and the cathode through the gas.

7. An electric system having, in combination, a gaseous-discharge device having an envelope containing a gas in which are disposed an anode and a cold cathode the major portion of which and of a surface thereof are constituted of about 85 to 99 parts tungsten uniformly sintered and bound together into a unitary mass with about 15 parts to 1 part, respectively, of barium oxide and with about 1 per cent of nickel, a relatively small cold-cathode spot being adapted to be formed on the said surface to produce the emission of electrons from the cold cathode at temperatures very substantially below the temperatures at which substantial thermionic emission may be produced from the cold cathode, a condenser, means for connecting the condenser to the anode and the cathode, means for charging the condenser, and means for discharging the condenser between the anode and the cathode to impress therebetween a brief voltage pulse of magnitude suflicient to form the relatively small cold-cathode spot on the said surface of the cold cathode but insuflicient to heat the cold cathode to a temperature at which substantial thermionic emission may be produced from the cold cathode, thereby to pass an electric discharge between the anode and the cathode through thegas.

KENNETH J. GERMESHAUSEN.

REFERENCES CITED The following references are of record in the file of this patent:

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